A spring washer having a spring property is known as a member that suppresses loosening of a fastener such as a screw or bolt. The loosening of the fastener is suppressed by widening the gap between the bearing surface of the fastener and the bearing surface of a member to be fastened by the spring property of the spring washer. The spring washer is usually a plain washer split at one point and twisted out of shape so that it has a spring property. The spring washer is crushed between the bearing surface of the fastener and the bearing surface of the member to be fastened, and the spring property is thereby exerted.
As a method for cooling an electronic component mounted on a board of an electronic device, there is known a method including fixing a heat sink thermally in contact with the electronic component to the board. Usually, the heat sink is fixed, in a state pressed against the surface of the electronic component, to the board so that heat is easily transferred from the electronic component to the heat sink. When the heat sink is fastened to the board, a spring washer is sometimes used for the purpose of suppressing loosening of a fastener.
However, when the heat sink (one of the members to be fastened) is fastened, in a state pressed against the electronic component, to the board (the other member to be fastened), the force pressing the heat sink against the electronic component may be excessive if the fastener is tightened until the spring washer is crushed. As a result, when the heat sink is fixed to the board, the load exerted from the heat sink may exceed the allowable load of the electronic component, and the electronic component may be damaged.
Related arts are disclosed in Japanese Laid-open Patent Publication Nos. 2000-199514 and 2001-187911.